Genetically determined resistance to collagenase action augments interstitial collagen accumulation in atherosclerotic plaques

Background - We hypothesized that collagenolytic activity produced by activated macrophages contributes to collagen loss and the subsequent instability of atheromatous lesions, a common trigger of acute coronary syndromes. However, no direct in vivo evidence links collagenases with the regulation of collagen content in atherosclerotic plaques. Methods and Results - To test the hypothesis that collagenases influence the structure of atheromata, we examined collagen accumulation in atherosclerotic lesions of apolipoprotein E-deficient mice (apoE^-/-) that express collagenase-resistant collagen-I (Col^R/R/apoE^-/-, n=12) or wild-type collagen-expressing mice (Col^+/+/apoE^-/-, n = 12). Aortic atheromata of both groups had similar sizes and numbers of macrophages, a major source of collagenases. However, aortic intimas from Col^R/R/apoE ^-/- mice contained fewer smooth muscle cells, a source of collagen, probably because of decreased migration or proliferation or increased cell death. Despite reduced numbers of smooth muscle cells, atheromata of Col ^R/R/apoE^-/- mice contained significantly more intimal collagen than did those of Col^+/+/apoE^-/- mice. Conclusion - These results establish that collagenase action regulates plaque collagen turnover and smooth muscle cell accumulation.